This invention relates generally to an electrophotographic printing machine, and more particularly concerns a recording member employed therein.
In the process of electrophotographic printing, a photoconductive member is charged to a substantially uniform level and exposed to a light image of an original document being reproduced. The light image discharges the photoconductive member in the irradiated areas to record an electrostatic latent image thereon. Thereafter, charged particles are attracted to the latent image so as to form a powder image on the photoconductive surface. The powder image is then transferred to a sheet of support material, i.e. the copy paper, in image configuration. The powder image adhering to the copy paper is then heated permanently affixing it thereto. This process is more fully described in U.S. Pat. No. 2,297,691 issued to Carlson in 1942 and further amplified by many other related patents in the art.
Since the time of the original disclosure of this process, the photoconductive member has required charging. Typically, this is accomplished by a corona generating device which sprays ions onto the photoconductive surface to achieve a substantially uniform charge thereon. Particles employed to develop the electrostatic latent image must have the correct polarity so as to be attracted thereto. It has become advantageous to both eliminate the charging process and to utilize uncharged insulating particles for the development process. One such approach modifies the recording member so as to eliminate the requirement for the charging step in the electrophotographic printing process. The foregoing is described in U.S. Pat. No. 3,288,602 issued to Snelling et al in 1966. This patent discloses one embodiment of a xerographic plate including a photoconductive layer adhering to a dielectric layer. Conductors are disposed in the dielectric layer contiguous with a support layer which is secured to the dielectric layer. The support layer or base may be insulating. An alternate embodiment is of a xerographic plate comprising a photoconductive layer having conductors disposed therein and contiguous with a dielectric layer adjacent to the photoconductive layer. A conductive layer, in turn, is secured to the dielectric layer. The dielectric layer is interposed between the photoconductive layer and the conductive layer. In both of the foregoing embodiments, an electrical potential is applied to the conductors so as to form a potential difference therebetween. This establishes an electrical field in the xerographic plate. A light image dissipates the electrical field in the irradiated areas to form a latent image which may be developed in the manner of all electrophotographic printing machines.
The structure of the present invention achieves a voltage varying pattern which attracts and holds uncharged insulating particles thereto. This structure is significantly improved over the prior art and attains higher resolution than was heretofore achievable.
Accordingly, it is a primary object of the present invention to improve the recording member employed in an electrophotographic printing machine so as to form a latent image thereon corresponding to an original document being reproduced which attracts and secures thereto uncharged insulating particles.